There are many theories about how the Great Pyramid in Egypt was constructed, ranging from UFOs to elaborate ramps and machines. But none has ever fully explained how mere human effort could raise such an incredible structure. Until now.

A French architect named Jean-Pierre Houdin has used 3D modeling software, combined with rigorous study of the pyramid itself, to advance a startling new theory that supported by some pretty compelling evidence.

Over at Archaeology, Bob Brier explains Houdin's theory. Basically, he suggests that the base of the pyramid was constructed using a ramp that was later dismantled and used to build a winding, spiral ramp on the inside walls of the pyramid. People carried stones up these ramps, building more ramp as they went. When they finished, the ramp was sealed within the pyramid walls. Writes Brier:

The architect has concluded that a ramp was indeed used to raise the blocks to the top, and that the ramp still exists—inside the pyramid!

The theory suggests that for the bottom third of the pyramid, the blocks were hauled up a straight, external ramp. This ramp was far shorter than the one needed to reach the top, and was made of limestone blocks, slightly smaller than those used to build the bottom third of the pyramid. As the bottom of the pyramid was being built via the external ramp, a second ramp was being built, inside the pyramid, on which the blocks for the top two-thirds of the pyramid would be hauled. The internal ramp, according to Houdin, begins at the bottom, is about 6 feet wide, and has a grade of approximately 7 percent. This ramp was put into use after the lower third of the pyramid was completed and the external ramp had served its purpose . . .

It may sound a little far-fetched, but Houdin points out that not only do internal structures in the pyramid match his descriptions, but an image taken of the pyramid's structure in the 1980s also backs up his theory:

When the French team surveyed the Great Pyramid, they used microgravimetry, a technique that enabled them to measure the density of different sections of the pyramid, thus detecting hidden chambers. The French team concluded that there were no large hidden chambers inside it. If there was a ramp inside the pyramid, shouldn't the French have detected it? In 2000, Henri Houdin was presenting this theory at a scientific conference where one of the members of the 1986 French team was present. He mentioned to Houdin that their computer analysis of the pyramid did yield one curious image, something they couldn't interpret and therefore ignored. That image showed exactly what Jean-Pierre Houdin's theory had predicted—a ramp spiraling up through the pyramid.

At left, you can see one of the microgravimetry images showing a structure that does look very much like a ramp hugging the inside walls of the pyramid.